Electron-emitting cathode and method of making the same



May 1, 1923. 1,453,267

J. L. BRADFORD ELECTRON EMITTING CATHODE AND METHOD OF MAKING THE SAMEFiled Nov. 29 1 v Y v I ATTORNEY Patented May I, 1923.

UNITED 4 STATES 1,453,267 PATENT OFFICE.

JAMES LLEWELLYN BRADFORD, OF NEW YORK, N. Y., ASSIGNOR TO DIE FORESTRADIO TELEPHONE & TELEGRAPH COMPANY, OF NEW YORK, Y., A. CORPORATION OFDELAWARE.

EDECTRON-EMITTING CATHODE AND METHOD OF MAKING THE SAME.

Application filed November 29, 1918. Serial No. 264,504.

To all 10770772 it may concern:

Be it known that I, JAMES L. BRADFORD, a citizen of the United States,residing at 'New York, in the county of Bronx, State of 5 New York, havemade a certain new and useful Invention in Electron-Emitting (lathodeand Method of Making the Same, of which the following is aspecification.

This invention relates to the manufacture of the'heated element, such asthe filament, or electron-emitting cathode member of an audion or vacuumtube, and particularly to the element referred to, as an article, aswell as to the method of making the same.

The object of the invention is to provide a filament orelectron-emitting cathode of greatly increased durability and constancyof activity, for use in audions or vacuum tubes.

A further object is to reduce the cost of manufacture of such deviceswhile securing greater length of life thereof, and increased efiiciency.

A further object is to provide an element of the nature. and for the usereferred to which requires less current in the use there of, therebyreducing the cost of operation of audions or vacuum tubes in connectionwith which the element is employed.

Other objects of the invention will appear more fully hereinafter.

The invention consists substantially in the structure and mode ofoperation hereinafter to be more fully setforth and described, asillustrated in the accompanying drawing, and finally defined in theappended claims. c i

In the construction of audions or vacuum tubes it is customary to emplovone or more cold electrodes and a hot electrode, the latter being calleda filament or electron-emitting cathode, and customarily heated by meansof an electric current traversing the same. Ordinarily, in the use ofthe device, the filament or electron-emitting element is heated to astate of incandescence in order to secure the highest degree of activityor electron-emission. This high degree of heat causes rapiddeterioration of the heated element and a consequent decrease in itsactivity. Various expedients have been proposed for increasing theactivity in the electron-emission and for heated element of an audion orvacuum tube. This expedient has not .proved to be entirely sat-isfactorand besides is quite expensive because 0 the use of a platinum base forthe coating.

I have found that all methods'which involve the application of coatingsare undesirable for the reason that filaments or cathodes so made arenot sufiiciently stable on permanent and gradually deteriorate, somemore rapidly than others, depending somewhat upon the nature of the baseemployed, the more expensive. bases, such as platinum being the best butopen to the objection of greater cost. In carrying out my invention Ipro ose to discard the idea of coatings, and, instead, to incorporatethe necessary ingredients intothe body of the material out of which thefilament or cathode is made. 'I have discovered that by combiningcertain suitable substances into an homogeneous mass with certainsuitable base materials, such mass can be worked into form to produce afilament or electronemitting cathode which is more stable and durable.than any heretofore proposed, which possesses a high degree of activityof electron emission, which possesses longer life in use than anyheretofore employed, which reouires only cheap material in itscomposition, and which requires reduced current for heating the same tothe desired degree for the desired extent of activity. I

In carrying out my invention I employ a suitable base material, and Ihave found that tungsten and molybdenum are well suited for thispurpose. I also employ suitable oxides and chlorides, preferably ofmetals of the alkali earth group, that is including those falling underthe second group and including the rare earth class of the eighth groupaccording to Mendelejefis periodic law. I have found that, forillusdients,-base, oxide and chloridein, powdered form, and the bestresults are secured when the ingredients are employed in the chemicallypure state. The base may be whollv tungsten, or molybdenum, or otherequivalent material, or a mixture of two or more of these substances. Inlike manner the oxides and the chlorides may be of separate elements ora mixture of two or more of them of the alkali earth group.

The oxide and chloride constituents, whether consisting of single oxideand chloride elements, or mixtures of oxides and of chlorides or theirequivalents, in powder form, are thoroughly mixed together, and themixture is then added to the base material and the whole composition isthen thoroughly mixed. Care should be taken in the mixing operation toavoid as much as possible abrasion or breaking up of the particles ofthe base material as that would tend to prevent the composition, in thesubsequent operations, from being drawn or formed into wire or filamentdimensions.

Without intending to be limited or restricted thereto the followingrelative proportions of the ingredients is given as illustrative of acomposition which I have found sufficient and satisfactory for thepurpose:

Example: Oxides and chlorides are mixed together in powdered form inabout the proportions as follows,--

60% of strontium oxide,

30% of barium peroxide,

, 10% ofpalladium chloride.

This mixture is then added to the base material in about the proportionas follows,-

5% by weight of the mixture of oxides'and chlorides,

95% by weight of the base material.

For convenience, I will call the mixture of the oxid-s and chloridsdiluents, or the rad io-active element.

the mass or pressed bar seem to amalgamate and form into an homogeneousbody, the time required in the heating operation varying somewhataccording to the nature and composition of the base material employed.

The homogeneous bar is then suitably swaged or drawn into the properdimensions to form a filament or cathode element for the purpose setforth.

The use of the chloride constituent increases the activity of thefilament or cathode as to its electron-emission properties.

I have found that when a filament or cathode, constructed in accordancewith my invention, is heated only to a dull red condition, an electronemission is secured to a degree of efficiency comparable with the bestfilaments heretofore employed in audions or vacuum tubes which areheated to incandescence to secure maximum activity. This means that lessheating current is required, and consequently there is lessdeterioration of the filament or cathode through oxidation or otherwise,thereby greatly prolonging the life of the filament or cathode withoutdecrease of its activity. I have also found that the electron-emissionactivity of the filament or cathode embodying my invention is moreconstant and uniform, and that the physical structure of the filament orcathode is more stable and stronger than those heretofore employed.

It will be observed that I avoid the use of platinum which is veryexpensive and adds materially to the cost of manufacture of filaments orcathodes, and, instead, I employ comparatively cheap materials and stillsecure greater longevity as well as advantageous results in the way ofmore stable and uniform emission, greater strength of filament orcathode, therefore less liability to become injured or broken inhandling or transporting the audions or vacuum tubes, less current forheating the element in use, and consequently securing economy not onlyin manufacture and upkeep, but also in operation of the audions orvacuum tubes employing the filament or cathode.

In the drawing I have shown a form of audion or vacuum tube asillustrative of the manner of use of an electrode, filament or cathodeembodying my invention, and wherein 1 is an evacuated vessel, 2 the basethereof, 3, 3 the plate or wing, and 4 the grid electrodes or elements,and 5 the hot member 0r element produced in accordance with my in- Illmating the mixture into an homogeneous body.

2. The process of manufacturing electronemitting cathodes, whichconsists in mixing together, a tungsten containing a base ma terial,with a diluent including oxides and a chlorid of metals of the alkaliearth group, and then amalgamating the mixture into an homogeneous body.I

' 3. The proces of manufacturing electronemitting cathodes, whichconsists 1n mixing together in powdered form a base material and adiluent including metallic oxides of the second group, and chlorids oftherare earth class of the eighth group of the periodic law, and thenamalgamating the 111mture into an homogeneous body.

' 4. The process of manufacturing electronemitting cathodes, whichconsists in mixing together tungsten and a diluent including metallicoxides and a chloride of the al- I I kali earth group, and thenamalgamating the mixture into an homogeneous body.

5. The process of manufacturing electronemitting cathodes, whichconsists in mixing together powdered tungsten and a diluent includingmetallic oxides and a 'chlorid of the alkali earth group, and thenamalgamating the mixture into an homogeneous body.

6. The process of manufacturing electronemitting cathodes, whichconsists in mixing together a base material and a mixtureof oxides and achloride of the alkali earth group, and finally amalgamating the mixtureInto an homogeneous body.

7. The process of manufacturing electronemitting cathodes, whichconsists in mixing together a mixture of base materials includingtungsten, an oxide and a. chloride ofthe alkali earth group, and thenamalgamating the mixture into an homogeneous body.

-8. The process of manufacturing electronemitting cathodes, whichconsists in mixing together tungsten and molybdenum as a base material,and an oxide and a chloride of metals of the alkali earth group, andthen amalgamating the mixture into an homogeneous body.

9. The process of manufacturing electronemitting cathodes, whichconsists in mixing together tungsten, and a diluent including strontiumoxide, barium peroxide and palladium chloride, and then amalgamating themixture into an homogeneous body.

10. The process of manufacturing electron-emitting cathodes, whichconsists in mixing to ether a base material, and a dilu-' ent includiing oxides and a chloride of metals falling under the second and eighthgroups respectively of the periodic law, and heatin the mixture to causethe ingredients thereo to form an homogeneous 'body. t

11. The process of manufacturing electron-emitting cathodes whichconsists in mixing together a base material, including tungsten, and adiluent including an oxide and a chloride of metals falling under thesecond and eighth groups respectively of the periodic law, and thencompressing the mixture and subjecting the compressed mass to heat toamalgamate the same into an homogeneous body. 7 I

12. The process of manufacturing ,electron-emitting cathodes whichconsists in mixing together a base material, and a diluent includingoxides and a chloride of metals falling under the second and eighthgroups respectively of the periodic law,- and heating the mixture to adegree below the melting point of the base material to amalgamate themass into anhomogeneous body.

13. The process of manufacturing electron-emitting cathodes whichconsists in mixing together a base material, and a diluentincluding anoxide and a chloride of metals falling under the second and eighthgroups respectively of the periodic'law, and

then compressing the mixture and subjecting the compressed mass to heatto a degree below that of the melting point of the base material toamalgamate the mass into an homogeneous body.

14. The process of manufacturing electron-emittin cathodes whichconsists in mixing toget er a base material, and a diluent including anoxide and a chloride of metals falling under the second and eighth grouprespectively of the periodic law, and then compressing the mixture andsubjecting the compressed mass to heat to amalgamate the same into anhomogeneous body, and finally drawing the heated body into thedimenslons to formthe cathode.

15. The process of manufacturing electron-emitting cathodes, whichconsists in mixing together a base material, and a diluent including anoxide and a chloride of metals falling under the second and eighthgroups respectively of the periodiclaw, andearths and palladiumchloride, and then amalgamating the mixture into an homogeneous body.

17. The process of manufacturing electron-emitting: cathodes whichconsists. in

mixing together a base material, a diluent including an oxide of a metalof'the alkali tron-emitting cathodes -which' consists in mixing togethera base material, a diluent including an oxide of a metal of the alkaliearths and palladium chloride, and then compressing the mixture andheating the compressed mass.

19. An electron-emitting cathode consisting of an homogeneous bodycontaining a base material, an oxide, and a chloride.

20. An electron-emitting cathode consisting of an homogeneous bodycontaining a base material, and a diluent including an oxide and achloride of metals of the alkali earth group.

21. An electron-emitting cathode consisting of an homogeneous bodycontaining tungsten as a base material, and a diluent including oxidsand a chloride of metals falling under the second and eighthrespectively roups of the periodic law.

22. n electron-emitting cathode consisttungsten and-molybdenum-as a basematerial, and a. diluent including oxids and a chloride of metalsfalling under-the second and eighth respectively. groups of the periodiclaw. I

23. Anelectron-emitting cathode consisting of an homogeneous bodycontaining a base material, a metallic oxide and palladium chloride.

24. An electron-emitting cathode consisting of an homogeneous bodycontaining a base material, strontium oxide and a metallic chloride.

25. An electron-emitting cathode consisting of an homogeneous bodycontaining tungsten, and a diluent including strontium ogiiide, bariumperoxide and palladium chlon e.

26. An electron-emitting cathode consistving of an homogeneous bodycontaining a base material, strontium oxide, barium peroxide and ametallic chloride.

In testimony whereof I have hereunto set my hand on this 23rd day ofNovember JAMES LLEWELLYN BRADI'URD.

